4 Common Causes of Generator or Switchgear Downtime (Michael Fluegeman, Antonio Tan III)

Overview

This article is the second part of a series by Michael Fluegeman and Antonio Tan III, published in FacilitiesNet / Building Operating Management in 2020. It covers four failure modes of standby generator systems: failure to start, failure to connect to the load, failure while running before utility returns, and failure to retransfer and shut down after utility returns. Each mode is paired with checks and tests on ATS settings, breakers, batteries, fuel and extended runs.

Fail-to-start causes include controls not in automatic, failed cranking batteries or chargers, and an ATS that never sends the start signal; the test is to de-energize the ATS normal source. Fail-to-connect causes include wrong ATS neutral-switch timing, a genset main breaker left open and breakers set at minimum, causing nuisance trips. The series thus shows that many failures stem from configuration and testing gaps rather than from the equipment itself.

Failures during the run are often fuel delivery or contamination problems; running on generator for several hours is suggested to prove extended operation. In the fourth mode, generators may run indefinitely after utility returns if ATS timers require manual retransfer or if the in-phase monitor or engine frequency prevents closed transition. In lightly staffed sites, an unnoticed post-outage run risks fuel exhaustion.

The article offers a practical, experience-based checklist; it does not give numerical thresholds or standard requirements. Related documents include NFPA 110 and NFPA 70. As a limit, detailed settings should be set according to manufacturer documents and local regulation. In design terms, generator and ATS catalogue entries should include start-signal logic, neutral timing and in-phase monitor settings, and the commissioning plan should include ATS transfer and retransfer tests and an extended loaded run.

Key points

1. Fail-to-start causes: controls not in automatic, failed cranking batteries or chargers, an ATS that never sends the start signal; test by de-energizing the ATS normal source.
2. Fail-to-connect causes: wrong ATS neutral-switch timing, genset main breaker left open and breakers set at minimum causing nuisance trips.
3. Failures during run are often fuel delivery or contamination problems; run on generator for several hours to prove extended operation.
4. Generators may run indefinitely after utility returns if ATS timers require manual retransfer or the in-phase monitor/engine frequency prevents closed transition.
5. In lightly staffed sites, an unnoticed post-outage run risks fuel exhaustion.
6. Related documents: NFPA 110 and NFPA 70.

Using it in design

• Include start-signal logic, neutral timing and in-phase monitor settings in generator/ATS catalogue entries.
• Include ATS transfer and retransfer tests and an extended loaded run in the commissioning plan.
• Warn if no remote monitoring of genset run status is specified for unmanned sites.
• Add cranking batteries and chargers explicitly to the maintenance programme.

Who should read it

Engineers and facility managers who design, commission and operate generators, ATS and switchgear.

Related standards

• NFPA 110
• NFPA 70

Publication details

Authors

Michael Fluegeman; Antonio Tan III

Publisher

FacilitiesNet / Building Operating Management

Year

2020

Document language

English

Source type

Expert / community

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation